The present invention relates to an organic optical recording medium which is recordable and readable by using a laser beam and useful as a medium for recording various information and images. The medium can take the form of an optical disc, an optical tape, an optical card, etc. More particularly, the present invention relates to an economical organic optical recording medium which is capable of achieving good processability and recording characteristics by employing a recording layer including an organic dye and a mixture of two or more polymers having different thermal properties.
With the explosion of a variety of information in accordance with an orientation toward an information-intensive society, recording media have been required to have increased data storage density and increased storage capacity. In correspondence to this need, research on the information recording medium having higher density, larger capacity and higher speed is actively pursued. In particular research is concentrated on the development of conventional magnetic recording medium and optical recording medium to have high density. However, research on ultra high densification through use of a novel optical recording material or a novel recording method is also actively pursued.
Japanese Laid-open Patent 60-20839, 62-109245 and 63-163341 disclose optical recording using photochromic material and optical recording using PHB (photochemical hole burning, Nikkei New Materials, Apr. 11th, 99, 1988) as a novel optical recording material. Though much concern was concentrated on the materials for ultra high densification, many problems still exist in practical use thereof. It is true that producing the material on a commercial scale seems difficult in the near future.
Therefore, recent studies on developing effective and economical methods for manufacturing the recording medium using the conventional method are in progress, rather than developing new recording materials or new recording methods. And the results of these studies gradually are being realized. CD-(Compact Disc-Recordable), the representative example, solves the most important problem of CD's, i.e., the problem of it being impossible to write information on the conventional CD, the CD-R enabling the user to record information. The CD-R can be played using a conventional compact disc player (CDP) and so demand for the CD-R is increasing. However, the CD-R disc should show high reflectivity of 70% or above to be compatible with conventional CD's. Accordingly, other CD-R discs, except for dye-type which was developed by Taiyo Yuden, have not been developed. See Japanese Laid-open Patent 63-179792, hei 1-206093 and hei 2-84384.
Meanwhile, besides optical discs which use dye as a recording material such as the CD-R disc, an optical magnetic disc using optomagnetic phenomena of metal and a metal phase change optical disc using the phase change of metal alloy, etc. have been developed. However, there are many difficulties associated with the preparation of these optical recording media as heavy metals are used and apparatus for vacuum deposition or sputtering, which is expensive and complicated, is required. These processes give rise to increased production cost and decreased productivity. Therefore, research on using organic material which is inexpensive and has good processability for the optical recording material has been pursued. See Japanese Laid-open Patent 57-46362, 58-197088 and U.S. Pat. No. 4,901,304.
However, most of the conventional recording methods using organic material employ thermal deformation or thermal decomposition of the recording material i.e., the organic material, by the heat generated during light exposure. In these methods, expensive curing resin is used as a recording material (see U.S. Pat. No. 4,901,304) or a large quantity of expensive dye is used for the thermal decomposition of the components (japanese Laid-open Patent 57-46362 and 58-197088), and then, the curing process is somewhat complicated.